1. Field of the Invention
The subject invention generally relates to a controlled-released composition for topical application to a substrate. The subject invention also generally relates to a method of delivering an active agent to the substrate. More specifically, the controlled-release composition and method of this invention incorporate an active agent into an oil-in-water emulsion for delivery of the active agent to the substrate upon application of the oil-in-water emulsion to the substrate.
2. Description of the Related Art
Oil-in-water emulsions and their uses are known across many industries. As one example, oil-in-water emulsions have been used throughout the medical industry as mediums for the controlled release of active agents. These oil-in-water emulsions more specifically include a silicone component, such as a silicone-based pressure sensitive adhesive, a surfactant, and water. It is known that the silicone component is generally highly viscous and difficult to process along with the surfactant and water. More specifically, the silicone component has a high elastic modulus and viscous modulus. Such Theological properties provide a resistance to deform and make the silicone component difficult to process along with the surfactant and water. Due to the high viscosity and other Theological properties of the silicone component in the oil-in-water emulsion, the processes by which silicone-containing oil-in-water emulsion can be produced have typically been limited to emulsion polymerization.
Other processes for producing the oil-in-water emulsion are known and include mechanical processes such as mechanical emulsification and mechanical emulsification by inversion. However, the oil-in-water emulsion can only be produced by these mechanical processes if the emulsion incorporates a solvent or solvents to essentially reduce or ‘cut’ the viscosity of the silicone component in the emulsion. Use of additional solvents to reduce the viscosity is undesirable in most applications due to a variety of reasons, such as health, safety, and environmental concerns.
Due to the inherent difficulties associated with producing oil-in-water emulsions by the mechanical processes without additional solvent, active agents have not, to date, been strategically incorporated into an oil-in-water emulsion that is substantially free of the additional solvents and that is produced according to the mechanical emulsification by inversion process referenced above. Furthermore, it is known that the active agents are typically difficult to uniformly incorporate, i.e., disperse, into the oil-in-water emulsion without any agglomerates. As a result, such emulsions have not been utilized as controlled-release compositions for topical application to a substrate, such as the skin of a human or animal. Nor have such emulsions been used as an instrument to deliver the active agent to the substrate.